Cottage-Style Scalloped Potatoes with Mushrooms

Rustic was exactly what we had in mind when conceiving this recipe. Mushrooms just seem to work in hearty, creamy baked dishes, don’t they?
Recipe by Jennifer of Ricotta and Radishes.
Prep Time: 20 mins. | Cook Time: 2 hrs.
Ingredients
For the sauce:
2 tbsp butter
2 tbsp all-purpose flour
3 cups milk
1/2 tsp salt
1 tsp black pepper
1 tsp garlic powder
For the potatoes and mushrooms:
1/2 Lb crimini or white button mushrooms
1 tbsp olive oil
1 medium onion, diced
4 Russet potatoes, thinly sliced
1/2 cup shredded Jarlsberg cheese
Salt and black pepper, to taste
Frank’s Red Hot, to taste
Method
For the sauce:
1. Heat the butter in a medium saucepan over medium heat. When the butter has melted and begins to bubble, whisk in the flour and stir vigorously until a paste forms. Cook for about 5 minutes, stirring constantly, until the flour is no longer ‘raw’ and has thinned out slightly. Reduce the heat to low and add the milk, whisking until fully incorporated; season with the salt, pepper and garlic powder. Simmer for 5 more minutes, cover and set aside.
For the potatoes and mushrooms:
1. Pre-heat oven to 375°F. Heat oil in a small pan over medium-high heat. Add the mushrooms and onions and cook, stirring, until mushrooms are browned and onions are softened, about 5 minutes. Season with salt and pepper and set aside.
2. Arrange one third of the sliced potatoes in a single layer in the bottom of a large casserole dish. Sprinkle one third of the mushroom mixture overtop and pour about one third of the cream sauce evenly over the first layer. Repeat to form two more layers and top with the shredded cheese. Cover dish with foil, transfer to the oven and cook for 60 to 90 minutes, or until potatoes are fork-tender and the cheese is golden brown.